What is the sensible heat factor (SHF)?

The sensible heat factor SHF is the ratio of the sensible cooling load to the total cooling load, SHF = Q_s/Q_t. Sensible heat changes the dry-bulb temperature while latent heat changes the humidity ratio. Typical office and residential cooling falls in the SHF = 0.65 to 0.80 range. Plotted on a psychrometric chart, the SHF line from the room state point shows the direction the cooling coil must process the air, making it the single most important indicator for coil selection.

Why does outdoor air intake lower the SHF so much?

Outdoor air adds both sensible (temperature difference) and latent (humidity difference) loads, but in hot humid summer conditions the latent component dominates. Processing 32°C/60%RH outdoor air down to 26°C/50%RH room air requires removing roughly 7.5 g of water per kilogram of dry air, which is energetically large. The result is a high latent fraction in the total load and therefore a much lower SHF.

Why is a low SHF difficult for coil selection?

A low SHF means the coil must dehumidify aggressively, so its surface temperature has to drop below the air dew point. Standard manufacturer coil rating tables assume SHF around 0.7 to 0.75; at significantly lower SHF the coil rows, fin spacing, chilled-water temperature, or face velocity must be adjusted, or a reheat or dedicated outdoor-air system (DOAS) must be added to handle the latent share separately.

How is the sensible-to-latent split for occupants chosen?

Occupant heat output depends on activity level and room temperature. For moderate office work, 65 W sensible and 60 W latent per person (125 W total) is a common reference. At higher room temperatures perspiration increases, raising the latent fraction; at lower temperatures the sensible fraction rises. For gyms and sports halls, total output exceeds 300 W per person with a heavy latent share, often producing SHF below 0.5.

Sensible Heat Factor (SHF) Calculator — HVAC Load Balance

Parameters

Occupants N

people

Lighting density

W/m²

Equipment density

W/m²

Floor area A

m²

Assumes outdoor air rate 30 m³/h per person (OAF≈20%), outdoor 32°C/60%RH, room 26°C/50%RH, occupants doing moderate work (65 W sensible, 60 W latent each).

Results

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Total sensible Q_s

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Total latent Q_L

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Total load Q_t

—

SHF = Q_s/Q_t

Load breakdown and SHF line on the psychrometric chart

Top: stacked bar of loads (occupant sensible/latent, lighting, equipment, OA sensible, OA latent). Bottom: simplified psychrometric chart with the SHF line from the room state toward the coil.

Theory & Key Formulas

Room cooling loads split into sensible heat (changes temperature) and latent heat (changes humidity). Their ratio SHF is the principal driver of coil design.

Sensible load Q_s. m_a is the air mass flow rate, c_p ≈ 1.006 kJ/(kg·K), ΔT the temperature difference:

$$Q_s = m_a \, c_p \, \Delta T$$

Latent load Q_L. Δw is the humidity-ratio difference, h_fg ≈ 2501 kJ/kg is the latent heat of vaporization:

$$Q_L = m_a \, \Delta w \, h_{fg}$$

Total load and sensible heat factor:

$$Q_t = Q_s + Q_L, \qquad SHF = \frac{Q_s}{Q_t}$$

A high SHF (≈0.8) indicates a dry load and a low SHF (≈0.5) a humid load. The slope of the SHF line on the psychrometric chart sets the coil processing direction.

What this SHF calculator does

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My senior engineer told me "this office has a low SHF, be careful." What is SHF exactly?

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Roughly speaking, it's the fraction of the total cooling load that goes into changing temperature, $\mathrm{SHF}=Q_s/Q_t$. The rest is latent load Q_L that removes moisture. With the default settings above the SHF lands around 0.47, which means the coil is doing more dehumidification work than sensible cooling. That's a low SHF.

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Why is there so much latent load? People in an office don't seem to produce that much moisture.

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The secret is outdoor air intake. The simulator assumes 30 m³/h per person of fresh air. Summer outdoor air at 32°C/60%RH carries about 18 g/kg of moisture, while the room at 26°C/50%RH holds about 10.5 g/kg. You have to condense out 7.5 g of water per kilogram of dry air — that's a huge latent load. Look at the bar chart: the red "OA latent" segment is the biggest by far.

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What happens to SHF when I move the occupant slider?

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Interestingly, adding people drives SHF further down. Each person contributes roughly half sensible and half latent, but the outdoor air rate scales with occupancy too, so the OA latent term grows fast. In contrast, more lighting and equipment is pure sensible load, which pushes SHF up. Try moving sliders and watching the four result cards together.

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Is that dashed cyan line on the chart the famous "SHF line"?

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Exactly, and it's the star of coil design. From the room state (yellow dot) it extends with a slope set by SHF. The cooling coil has to process the air along this line. The green dot is the apparatus dew point, where the SHF line meets saturation — that's roughly the coil surface temperature you need. A lower SHF means a steeper line and a lower coil surface temperature.

Frequently Asked Questions

General office and residential cooling falls in SHF = 0.65 to 0.80. Densely occupied meeting rooms with high outdoor-air rates land at 0.55 to 0.65. Gyms, commercial kitchens, and humid factories sit at 0.40 to 0.55. Server rooms and dry industrial spaces can exceed 0.90. The default inputs of this tool produce SHF ≈ 0.47, a realistic high-latent-load case.

On a psychrometric chart, draw a line from the room design point with slope dictated by SHF and pick the coil leaving-air state somewhere along it. Once the leaving-air temperature is fixed, the coil's sensible and latent capacity requirements are determined. A steep SHF line points to a dehumidification-dominated coil; a shallow line points to a sensible-cooling-dominated coil.

Standard chilled-water coils work best around SHF ≈ 0.7. When SHF drops below 0.5 it usually pays to switch strategy: subcool-and-reheat schemes, desiccant dehumidification, or a separate sensible/latent system (DOAS coupled with sensible terminals) become competitive. The choice trades dehumidification capacity against energy use.

Summer design with 32°C/60%RH outdoor and 26°C/50%RH indoor, 30 m³/h per person of outdoor air (≈20% OAF), moderate-work occupants (65 W sensible, 60 W latent each), and lighting plus equipment treated as 100% sensible. Real designs also include envelope conduction, fan heat, infiltration, and time-varying schedules. Use this calculator to build intuition for SHF, then refine with a full hour-by-hour load simulation.

Real-world applications

Office and commercial HVAC: AHU selection for offices, retail and hotels starts by estimating SHF from occupancy and ventilation. When SHF drops below 0.6, reheat coils (CAV/VAV) are often added to keep indoor humidity in check. Meeting halls and lecture theatres see SHF swing strongly with occupancy, so variable-air-volume control and mode switching matter.

Data centres and precision cooling: Server rooms are nearly all sensible load with minimal outdoor-air intake, pushing SHF to 0.9 or above. Dry-coil operation — keeping the coil above the dew point — saves energy and avoids condensation. SHF analysis is the starting point for coil and chilled-water temperature selection.

Kitchens, pools, and gyms: Steam, sweat, and evaporation can drive latent load above sensible. SHF below 0.4 is common, calling for desiccant dehumidifiers or reheat schemes. Use this tool to get a rough SHF and decide whether a standard package unit is even feasible.

Building energy CAE: Building energy simulators such as EnergyPlus and TRNSYS report hourly SHF. Knowing how occupants, lighting, equipment and outdoor air each push SHF up or down makes it much easier to interpret those outputs and validate AHU sizing.

Common misconceptions and pitfalls

The most common mistake is thinking "as long as I hit the room setpoint, I don't need to worry about SHF." But SHF is the direction vector telling the coil how to get there — the path matters as well as the endpoint. If your site really has SHF = 0.5 but you size a coil assuming SHF = 0.75, the room temperature can stabilize while humidity stays uncomfortably high. Always check SHF and the load breakdown before locking in equipment.

Next is under-counting outdoor air. Even at code-minimum ventilation rates, OA latent can dominate, as the simulator shows. The 30 m³/h per person assumed here is a baseline office value; meeting rooms, classrooms, and post-pandemic enhanced ventilation can demand two to three times that. As you raise the occupant slider, the red OA segments grow almost linearly and SHF drops. That's why dedicated outdoor air systems (DOAS) handling ventilation latent load separately are now standard in many designs.

Finally, do not freeze SHF at a single value. SHF varies by hour, season, and operating mode. Morning warm-up has cool dry outdoor air and high SHF; peak afternoon brings high occupancy and humid outdoor air, lowering SHF; night setback with no occupants is internally driven and runs at high SHF. Design for the peak SHF, but also evaluate the annual SHF range so that your variable-capacity control (inverter compressors, VAV, reheat modulation) can keep both comfort and efficiency in line across the whole spectrum.

Sensible Heat Factor (SHF) Calculator — HVAC Load Balance

What this SHF calculator does

Frequently Asked Questions

Real-world applications

Common misconceptions and pitfalls

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